In recent years, a large number of biological/chemical analysis techniques have been demonstrated using micro-scale systems and have been implemented using micromachining technology. The rationale for using microscale technologies in analytical instrumentation includes reduction in instrument size and cost, reduction in sample and reagent volume, reduction in analysis time, increase in analysis throughput, and the possibility of integration of sample preparation and analysis functions.
Currently, high spot density arrays are produced using robotic spotter systems, such as the GENETIX QARRAY®. One of the current techniques uses spotting “pens” which collect the material to be deposited on a needle and then “spots” the material on to a substrate. See, e.g., U.S. Pat. No. 6,733,968 to Yamamoto et al., (“'968 patent”) entitled “Microarray, Method for Producing the Same, and Method for Correcting Inter-Pin Spotting Amount Error of the Same.” The '968 patent notes that when multiple “pens” are used to create an array, not all of the “pens” are microscopically the same size, and therefore each “pen” blots a different amount of solution. The patent discloses a method for determining what the errors are for a given set of “pens” so the errors can be mathematically accounted for.
U.S. Pat. No. 6,365,349 to Moynihan et al., entitled “Apparatus and Methods for Arraying Solution onto a Solid Support,” discloses the use of a spring probe to administer samples onto a substrate.
Similar to the use of “pens” is the use of capillaries. See e.g., U.S. Patent Application 20040014102, Chen et al., entitled “High Density Parallel Printing of Microarrays.” The application discloses the use of capillaries to spot samples onto a microarray. U.S. Pat. No. 6,594,432 to Chen et al. (“'432 patent”), entitled “Microarray Fabrication Techniques and Apparatus,” also discloses the use of capillaries, such as silica tubes, to spot probes onto a substrate. In the '432 patent, one end of the capillaries may be attached to a reservoir; however there is no return path for the substance that is spotted and therefore no way to flow a substance over a substrate to increase the spot deposition density. The capillary action of the '432 patent is therefore similar to that done with pens. For an additional example see, U.S. Pat. No. 6,110,426 to Shalon et al., entitled “Methods for Fabricating Microarrays of Biological Samples,” which discloses a method for tapping a meniscus at the end of a capillary tube to deliver a specified amount of sample material onto a substrate.
While prior art systems are capable of producing multiple spots of a controlled size, if the desired molecule for deposition is present in very low concentration, the total number of desired molecules that can be deposited on the surface is severely limited for a single spot. The concentration of material in the spots is limited by the concentration of the original material and the spot size. The Perkin-Elmer BIOCHIP ARRAYER® uses “ink jet printing” technology, but that method has the same concentration limitation as the “pens.”
Other systems have been developed which use microfluidic channels on a substrate to pattern genes, proteins, nucleic acids, such as RNA, DNA, oligonucleic acids, or other arrays. For an example of such a system see, U.S. Pat. No. 6,503,715 to Gold et al., entitled “Nucleic Acid Ligand Diagnostic Biochip.” Biochip fabrication methods have been developed that attempt to stir individual microassay spots; however, such systems often require mechanical manipulation of the biochip. See e.g., U.S. Pat. No. 6,623,696 to Kim et al., entitled “Biochip, Apparatus for Detecting Biomaterials Using the Same, and Method Therefor,” which discloses spinning a biochip in order to accelerate reaction time. A need exists to simplify the process of developing biochips and biosensors and for providing more control over individual spots on the biochips and biosensors.
Ideally, a flow deposition system could produce a high surface density if the substrate surface were tailored to bond only to the desired molecules, allowing the unwanted bulk material to be washed away. However, flow deposition systems generally are incapable of producing spot arrays, let alone individually addressed arrays. See, e.g., Japan Patent Application 10084639, Tomoko et al., entitled “Method and Apparatus for Adding Sample.” That application discloses a method wherein a biochip is rotated and centrifugal forces are used to uniformly spread a sample over the entire surface of the biochip. Similarly, U.S. Pat. No. 6,391,625 to Park et al., entitled “Biochip and Method for Patterning and Measuring Biomaterial of the Same,” discloses a method for making biochips via irradiating portions of the substrate with a laser and then spin coating probe molecules onto the substrate.
Additionally, current technology is unable to sequentially chemically process individual spots, or to perform layer-by-layer self-assembly (LBL) to build up the spot concentration. What is needed is a way to take molecules in a solution and adhere a high-concentration of those molecules on a substrate. This would be particularly advantageous in studying protein function.
Additionally, microarray-type structures are used in forming biosensors and the same problems associated with biochips apply to biosensors. See e.g., U.S. Pat. No. 6,699,719 to Yamazaki et al., entitled “Biosensor Arrays and Methods,” which discloses using microarray forming techniques in the formation of a biosensor. A need exists to simplify the creation the biosensors.
A need exists to decrease the cost and time involved in processing microarrays as well. Attempts have been made to address that need, see e.g., U.S. Patent Application 2003/0068253 A1, Bass et al., entitled “Automation-Optimized Microarray Package,” which discloses a method for automating microarray processing via a linear strip of microarrays that is processed in an assembly line fashion. Lab-on-a-chip microfluidic devices have included sample wells directly above microfluidic channels; however, a need exists to simplify the cost and time of loading those sample wells.